Last Updated April 19th
Caspian Tern Colony Counts East Sand Island As of 16 April, no Caspian tern eggs had been observed on the East Sand Island colony. In 2005 the first egg at the East Sand Island tern colony was seen on 14 April, the earliest lay date so far recorded for Caspian terns in the Columbia River estuary, and in 2004 the first egg was seen on 16 April. Caspian tern nesting chronology this year on East Sand Island is somewhat delayed compared to 2004 and 2005, a delay that is apparently weather-related.
During this past week, no terns were observed roosting or attempting to nest in upland areas of Rice Island, Miller Sands Spit, or Pillar Rock Sands (dredged material disposal islands in the upper estuary). We will continue to monitor Rice Island and the other upper estuary dredged material disposal islands for early signs of nesting (e.g., nest scrape digging) and will promptly inform resource managers of any such activity.
The high and low on-colony counts for the week on Crescent Island were 343 terns (13 April) and 179 terns (11 April), respectively. The numbers of Caspian terns on the Crescent Island colony are slightly less than at this time last year. As of 16 April, no tern eggs had been observed at the Crescent Island colony. In 2004 and 2005 the first tern eggs were observed on the Crescent Island colony on 12 April. Like the East Sand Island colony, the nesting chronology of the Crescent Island colony is somewhat delayed compared to the last two years. Nesting Caspian terns have not been observed at other sites along the Mid-Columbia River.
For the week, 43% of the identifiable fish delivered to the Crescent Island tern colony (N = 79) were salmonids. This compares to 79% salmonids in the diet at this time last year.
At East Sand Island, bald eagles have been observed at the colony throughout the week, frequently causing terns to take flight. As many as seven eagles have been observed on the island at one time. One subadult eagle landed briefly on the tern colony. A total of 25 colony disturbances were observed (all causes) at a rate of 0.7 disturbances/hr of observation. Generally, these disturbances are short, causing terns to flush for only 10-30 seconds before returning to the colony. There was one disturbance observed at the Crescent Island tern colony this past week at a rate of 0.1 disturbances/hr of observation.
To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.
There were no visitors in the field this past week. |
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The high and low on-colony counts for the week on East Sand Island were 5,181 terns (14 April) and 1,304 terns (10 April), respectively. The number of terns on colony this week was similar to counts conducted at the colony this time last year. The colony has continued to increase in size despite the wet and cool weather in the estuary. Three inches of rain have fallen in Astoria so far this April. This has resulted in some standing water on the East Sand Island tern colony, with the majority of the colony area appearing wet following periods of heavy rainfall. After heavy rains subside, most of the standing water drains from the colony within a few hours. One exception is an area on the upper half of the colony (west end), which has taken longer to drain. During this time of the year, we have observed similar flooding on the colony in previous years. 
For the week of 10–16 April, 25% of the identifiable fish delivered to the East Sand Island colony (N = 362 prey items) were salmonids. This compares to 27% salmonids in the diet at this time last year. At least some of the salmonids that came into the colony this week were coho salmon that were released from net pens in Youngs Bay this past week. The majority of the prey items being delivered to the East Sand Island colony were clupeids (i.e., herring or sardines; 39%). 
This past week, gull kleptoparasitism rates at East Sand Island were 1% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates were 4% of all known fates of fish delivered by terns this past week. At the East Sand Island tern colony, kleptoparasitism is by glaucous-winged/western gulls, while at Crescent Island kleptoparasitism is by the smaller California gull.